Linear motion devices

ABSTRACT

Apparatus for producing linear motion comprising a coil defining an electromagnetic field across a gap; and a permanent magnet disposed within the magnetic field in the gap and arranged to be driven in motion by the magnetic field, the permanent magnet being configured such that its axis of magnetization lies along its smallest dimension.

FIELD OF THE INVENTION

The present invention relates to electromagnetic drive apparatus andmore particularly to electromagnetic devices producing linear motion.

BACKGROUND OF THE INVENTION

Various types of linear motors are known in the art and are used forsuch diverse functions as driving a phonograph turntable and operating acompressor. There is shown in Austrian Pat. No. 195558 and in an articleby G. Perronne, entitled "Compresseurs Electromagnetiques Oscillants"appearing in the Bulletin Annexe (Suppl. 2) of the InstitutInternational du Froid, 1958, Vol. 2, pp. 267-278, a compressor whichemploys a pair of oppositely magnetized permanent magnets disposedwithin the gap of an AC electromagnet. The magnets are spaced from eachother along an axis extending through the gap and move in reciprocalmotion along that axis. Although no information as to the efficiency ofsuch compressors is available from the above references, it appears thatthey are relatively inefficient and require relatively high powerelectrical inputs.

SUMMARY OF THE INVENTION

The present invention seeks to provide a linear motor of relatively highefficiency which is suitable for powering a wide range of devices, whiledrawing relatively small amounts of power.

There is thus provided in accordance with an embodiment of the inventionapparatus for producing linear motion comprising: a coil defining anelectromagnetic field across a gap; and a permanent magnet disposedwithin the magnetic field in said gap and arranged to be driven inmotion by the magnetic field, the permanent magnet being configured suchthat its axis of magnetization lies along its smallest dimension.

In accordance with a preferred embodiment of the invention, thepermanent magnet comprises first and second sections, magnetized inrespective opposite directions and securely joined together to define asingle body or formed of a unitary element. The relative orientation ofthe two oppositely-magnetized sections determines the axis of motion ofthe permanent magnet in a plane perpendicular to the axis ofelectromagnetic flux across the gap. The provision of an AC current tothe permanent magnet causes the permanent magnet to undergo oscillatorymotion.

Oscillatory motion of amplitude greater than the dimensions of theoppositely magnetized sections of the permanent magnet may be providedby an array of joined oppositely magnetized sections disposed inassociation with a plurality of fixed electromagnets in a desired out-ofphase arrangement. Suitable commutator apparatus, such asphotodiode-operated relays for switching the field directions arerequired.

According to an embodiment of the invention employing a singlemagnetized section, vibrating systems exhibiting parametric excitationcan be realized.

It is a particular feature of the invention that significantly higherefficiency is realized in accordance with the present invention ascompared with prior art devices such as those described in the abovereferences, as the result of the consideration of leakage flux. Thisconsideration, absent in the prior art references, suggests an optimalrelationship between gap separation and thickness of the permanentmagnet along the axis of its magnetization.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood and appreciated from thefollowing detailed description taken in conjunction with the drawings inwhich:

FIG. 1 is a schematic illustration of a portion of a linear motionmechanism constructed and operative in accordance with an embodiment ofthe invention;

FIG. 2 is a schematic illustration of a linear motion mechanism of thesame type as that illustrated in FIG. 1;

FIG. 3 is a schematic illustration of a linear motion mechanismconstructed and operative in accordance with an alternative embodimentof the invention;

FIG. 4 is a schematic illustration of a balanced center-of-gravitylinear motion mechanism constructed and operative in accordance with anembodiment of the invention;

FIG. 5 is a schematic illustration of a linear motion mechanismconstructed and opeative in accordance with still another alternativeembodiment of the invention;

FIG. 6 is a schematic illustration of a balanced center-of-gravitylinear motion mechanism constructed and operative in accordance with analternative embodiment of the invention;

FIG. 7a is an illustration of a generally circularly configured linearmotion mechanism constructed and operative in accordance with anembodiment of the invention;

FIG. 7b is an illustration of a portion of the linear motion mechanismof FIG. 7a;

FIGS. 8a and 8b illustrate two variations of laminated permanent magnetsusable in the linear motion mechanisms of the present invention;

FIG. 9a is a schematic top view illustration of a linear motionmechanism constructed and operative in accordance with an embodiment ofthe invention;

FIG. 9b is a sectional illustration of a portion of the mechanism ofFIG. 9a taken along the lines A--A;

FIG. 10 is a schematic illustration of a linear motion mechanismconstructed and operative in accordance with an embodiment of theinvention;

FIG. 11 is a schematic illustration of a linear motion mechanismconstructed and operative in accordance with another embodiment of theinvention;

FIG. 12 is a schematic illustration of a scaled-up version of a linearmotion mechanism constructed and operative in accordance with anembodiment of the invention;

FIG. 13 is a schematic illustration of four stages in the operation of alarge amplitude linear motion mechanism constructed and operative inaccordance with an embodiment of the invention;

FIG. 14 is a schematic illustration of a portion of a linear motionmechanism constructed and operative in accordance with an embodiment ofthe invention;

FIG. 15 is a schematic illustration of a scaled up linear linear motionmechanism constructed and operative in accordance with an embodiment ofthe invention; and

FIGS. 16A and 16B are respective side sectional and end views of acompressor constructed and operative in accordance with an embodiment ofthe present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Reference is now made to FIGS. 1 and 2 which illustrate, with differingdegrees of generality, a linear motion mechanism constructed andoperative in accordance with an embodiment of the invention.

It is noted at the outset that although the invention will be describedwith reference to specific examples operative as linear drive devices,the invention is sufficiently general to include generators whichproduce an electrical current in response to an applied lineardisplacement of a permanent magnet. The terms linear motion device andlinear motion mechanism will therefore be used to denote generators aswell as motors.

A gap 10 is defined by a conventional AC electromagnet 12. Magnetic fluxis produced by the electromagnet across gap 10 along an axis 13.Electromagnet 12 comprises an iron core 15 around which are wound coils17. The coils are coupled to an AC source 19 across a capacitor 21,provided to increase the power factor of the device. The coils may alsobe coupled to a D.C. voltage source across a resistance 23. Iron core 15is preferably formed of a plurality of relatively thin layers laminatedtogether. The laminations may be stacked along axes perpendicular to theflow of magnetic flux, so that the effects of eddy currents are reduced.One arrangement of stacked layers is illustrated in FIG. 1 while anotherpossible arrangement is illustrated in FIG. 3.

Disposed in gap 10 for motion along an axis 11, lying perpendicular tomagnetic flux axis 13, is a permanent magnet 14. In the illustratedembodiment, permanent magnet 14 is of generally sheet-like configurationand is magnetized along an axis perpendicular to the plane thereof.Permanent magnet 14 is formed of oppositely magnetized first and secondportions 16 and 18 which are either formed of an integral piece offerromagnetic material or alternatively are joined together as byadhesive. The two portions may be in touching engagement oralternatively spaced from each other by a desired amount of spacing.Additional structural strength may be achieved by laminating a plasticsheet 20 on both planar surfaces of the permanent magnet, as illustratedin FIG. 1.

As seen in FIG. 2, permanent magnet 14 is dimensioned to extend beyondgap 10 so as to avoid the balancing of magnetic forces thereon.Permanent magnet 14 may be mounted by means of springs 22 onto a support24 mounted onto electromagnet 12. Springs 22 and support 24 are arrangedto permit coupling of a drive shaft 26 onto permanent magnet 14 fordriving engagement therewith.

It is appreciated that the permanent magnet moves to align the directionof magnetization thereof with the direction of the magnetic flux at anygiven time. In the illustrated embodiment, the permanent magnet 14 willmove along axis 11 in a direction so as to maximize the overlap betweenthe magnetic flux and the portion of the permanent magnet magnetizedco-directionally therewith.

Thus during AC operation of the electromagnet, where the magnetic fluxchanges direction along axis 13, the permanent magnet undergoes periodicreciprocal motion along axis 11 as alternatively first and secondportions align themselves with the flux. The directions of magnetizationof the first and second portions are indicated by arrows 25 and 27respectively.

It may be readily appreciated that if permanent magnet 14 wererepositioned by ninety degrees in its plane so that portions 16 and 18were positioned in side-by-side orientation instead of the up-downorientation illustrated in FIGS. 1 and 2, the axis of motion thereofwould be displaced by ninety degrees to an axis 28, lying perpendicularto both axes 11 and 13. This alternative orientation of the portions ofthe permanent magnet has the advantage that the amplitude of motion ofthe permanent magnet is not limited by the propinquity of the bottomportion of the U-shaped electromagnet 12. The side-by-side orientationinvolves certain complications when it it is sought to employ aplurality of similar electromagnets side-by-side in a scaled-upembodiment. This embodiment will be described later in the presentspecification.

Permanent magnet 14 should be of the oriented type and must be of highcoercivity _(I) H_(C), typically above 3000 oersted and must be of highremanence, typically above 3000 Gauss. Preferably the hysteresis lossassociated with the minor loop traversed by the material during ACoperation should be small. One example of a material suitable forconstruction of the permanent magnet is RAECO-16, manufactured by theRaytheon Corporation of the U.S.A.

Although permanent magnet 14 is normally centered with the divisionbetween first and second portions 16 and 18 at the center of gap 10, itmay alternatively be maintained off center by suitable selection of aD.C. input voltage to the electromagnet. This adjustability may beuseful where the linear motion device is used to power equipment wherethe average or peak position of the moving member should be adjustable.

Reference is now made to FIG. 3 which shows a linear motion devicesimilar in all relevant respects to that illustrated in FIG. 2 except inthat it comprises a spring mounted permanent magnet 29 which isuniformly magnetized in a single direction. During AC operation of theelectromagnet 31, permanent magnet 29 moves in reciprocal motion alongan axis 33, perpendicular to the magnetization direction of thepermanent magnet indicated by an arrow 35. This linear motion deviceoperates in a parametric excitation regime at periodicities which aremultiples of one-half of the excitation frequency. The spring isselected such that the resonance frequency of the vibrating system isone of the above multiples.

Eddy current losses in the permanent magnet may be reduced by the use oflaminated constructions for the permanent magnets.

Reference is now made to FIGS. 8a and 8b which illustrate twoalternative variations of permanent magnets formed by laminating orotherwise joining together a plurality of layers of magnetic materialsuch as RAECO-16. In both cases, and in all cases of laminated magnetsof interest here, the layers are stacked along axes perpendicular to theaxis of magnetic flux of the electromagnet along which lie thedirections of magnetization of the portions of the permanent magnetsindicated by arrows 30 and 32 respectively. It may be appreciated thatthe embodiment illustrated in FIG. 8b has an advantage in theconstruction of permanent magnets having oppositely magnetized portions.In this embodiment the junction between the oppositely magnetizedportions may be realized by an ordinary, or possibly strengthened,lamination.

An alternative embodiment of the invention, particularly suitable forapplications in which co-ordinate motion of a pair of members isrequired, such as electrically powered scissors or clippers, isillustrated in FIG. 4. A conventional AC electromagnet 40, similar inall relevant respects to electromagnet 12 defines a gap 42. Disposedwithin gap 42 are first and second permanent magnets 44 and 46, bothmagnetized in the same direction as indicated by arrows 48 and 50.Permanent magnets 44 and 46 are each separately coupled by means (notshown) to driven means, such as opposing blades of a scissors or clippermechanism.

During AC operation of electromagnet 40, when the direction of themagnet flux is along arrows 48 and 50, permanent magnets 44 and 46 movetogether towards the center of the gap. When the direction of themagnetic flux is opposite to that indicated by arrows 48 and 50,permanent magnets 44 and 46 move away from each other. The axis ofreciprocal motion of permanent magnets 44 and 46 are perpendicular tothe axis of magnetic flux and are indicated by arrows 52. It is notedthat the motion of permanent magnets 44 and 46 is such that their centerof mass remains substantially static.

Reference is now made to FIG. 5 which illustrates a linear motionmechanism constructed such that the motion of the permanent magnet isnot limited by the presence of the iron core of the electromagnet. Herea permanent magnet 60 formed of oppositely magnetized portions 62 and 64and similar in all relevant respects to permanent magnet 14 of FIGS. 1and 2 is disposed within a gap 66 defined between the center arms 68 ofan AC electromagnet 70. In the exemplary embodiment illustrated in FIG.5 the electromagnet comprises a core in the general shape of a closedrectangular having central arms which are spaced from each other. Coils72, only one of which is shown in FIG. 5 for the sake of clarity, arewound about the central arms 68 and are coupled to power sources in amanner similar to the connection of electromagnet 12 described inconnection with FIG. 2 hereinabove.

During AC operation of the electromagnet, magnetic flux is generatedacross gap 66 along an axis 74 along which are magnetized portions 62and 64 of permanent magnet 60. The changes in direction in magnetic fluxcause permanent magnet 60 to undergo periodic reciprocal motion along anaxis 76 perpendicular to axis 74.

It is noted that the side-by-side orientation of the portions 62 and 64of permanent magnet 60 results in motion which is not limited by thegeometry of the electromagnet core since the travel path of thepermanent magnet along axis 76 does not intersect any of theelectromagnet structure. The embodiment of FIG. 5 is also characterizedby the presence of relatively small fringing fields, thus enhancing theelectromagnetic compatibility and increasing the magnetic efficiency, ascompared with the prior art. The embodiment of FIG. 5 also displays agreater structural rigidity and resistance to fatigue than typicalC-shaped embodiments, such as that illustrated in FIG. 3.

Referring now to FIG. 6 there is seen another embodiment of a staticcenter of mass linear motion mechanism constructed and operative inaccordance with an embodiment of the invention. A pair of generallyC-shaped electromagnets 80 and 82 are joined together in fixed spatialrelationship by means of securing members 84 and 86. Each ofelectromagnets 80 and 82 is formed of a C-shaped soft iron core whichdefines a gap 88. Adjacent the gap are disposed coils 90 and 92. Coils90 and 92 are connected to an AC power source in parallel in-phaserelationship such that electromagnets 80 and 82 operate identically andin phase.

Disposed in gap 88 of electromagnet 80 and extending therebeyond is apermanent magnet 94 comprising oppositely magnetized portions 96 and 98.Similarly disposed in gap 88 of electromagnet 82 and extendingtherebeyond is a permanent magnet 100 comprising oppositely magnetizedportions 102 and 104. Adjacent portions 98 and 102 of respectivepermanent magnets 94 and 100 are magnetized in the same direction,indicated by arrows 106, while exterior portions 96 and 104 ofrespective permanent magnets 94 and 100 are also magnetized in anidentical direction, indicated by arrows 108 and being opposite to thedirection indicated by arrows 106.

Permanent magnets 94 and 100 are mounted on respective springs 110 and112 which are attached to the cores of respective electromagnets 80 and82.

It is appreciated that during in phase AC operation of electromagnets 80and 82 respective permanent magnets 94 and 100 engage in periodicreciprocal motion either towards or away from each other and such thatthe center of mass of the permanent magnets remains substantiallystatic.

In the illustrated embodiment and in the embodiment of FIG. 2 it isdesirable that the springs supporting the permanent magnet be selectedto reach their resonance at the desired operating frequency and normallyto center the permanent magnet in the gap.

Reference is now made to FIGS. 7a and 7b which illustrate a linearmotion mechanism constructed and operative in accordance with anembodiment of the invention and employing a curved permanent magnet. Agenerally disc shaped electromagnet 120 is illustrated in cut-awaypictorial view defining a generally circular gap 122 in which isdisposed a permanent magnet 124 of generally circular cross section.

Permanent magnet 124 is formed of first and second generally cylindricalportions, magnetized in opposite directions, arranged to define upperand lower rings 126 and 128 whose magnetization directions are indicatedby respective arrows 130 and 132. Inner and outer coils 134 and 136 aredisposed in a generally annual recess centered beneath gap 122 and arecoupled to an AC source by means not shown. The configuration ofelectromagnet 120 is defined by a generally annular core desirablyformed of high resistivity, low lose transformer iron or a similarmaterial.

According to a preferred embodiment of the invention the core is formedby laminating a multiplicity of thin segments 140, such as thoseillustrated, not necessarily to scale, in FIG. 7b. It is noted that thelaminated construction in this and other embodiments illustrated hereinwhich serves to greatly reduce effects of eddy currents.

During AC operation of the electromagnet 120, permanent magnet 124 movesin periodic reciprocal motion along an axis 142 extending perpendicularto the magnetic flux lines across the gap.

According to an alternative embodiment of the invention representing avariation of the embodiment illustrated in FIGS. 7a and 7b, anelectromagnet may be formed to define a generally conical gap and asuitably configured permanent magnet having oppositely magnetizedportions may be disposed therein for motion relative thereto.

It may be appreciated that the embodiment illustrated in FIGS. 7a and 7brepresents the end point of a generalization of the linear motionmechanisms of the invention to multi-gap embodiments. Instead ofemploying a circular gap and a circular cylindrical permanent magnet asin the embodiment of FIG. 7a, one may employ a rectangular cylindricalpermanent magnet and four separate electromagnets. As a furtheralternative a plurality of separate permanent magnets may be joinedtogether either conductively or insulatively for common movement eachrelative to a corresponding electromagnet. Such an embodiment isillustrated in FIGS. 9a and 9b.

Referring now to FIGS. 9a and 9b it is seen that four electromagnets 150are disposed at a ninety-degree separation from one another to define agenerally rectangular arrangement. The electromagnets may beconventional electromagnets such as that illustrated in FIG. 2 and arecoupled to an AC power source in a manner similar to the coupling of theelectromagnet in FIG. 2 and such that all of electromagnets 150 operatein phase with each other.

Electromagnets 150 each define a gap 152 in which is disposed apermanent magnet 154 having oppositely magnetized portions 156 and 158,as illustrated particularly in FIG. 9b. During AC operation of theelectromagnets 150, permanent magnets 154, which are rigidly joinedtogether by coupling members 160, undergo periodic reciprocal motionalong an axis 162.

Reference is now made to FIG. 10 which illustrates a linear motiondevice comprising a generally annular electromagnet 170 having acentrally disposed coil 172 and defining a generally cylindrical gap 174across which the magnetic flux lines extend along an axis 176. Agenerally elongate permanent magnet 178, which may be cylindrical asillustrated or of any other suitable configuration, is disposed withinan axial passageway defined at the center of electromagnet 170.

Permanent magnet 178 comprises first and second oppositely magnetizedportions 180 and 182 and may be formed of high remanence ferromagneticmaterial such as RAECO-16. It is noted that portions 180 and 182 aremagnetized in opposite directions along axis 176, indicated by arrows184 and 186.

Coil 172 is coupled to a source of alternating current, preferablyacross a capacitor, not shown, and in a manner similar to the couplingof electromagnet 12 of FIG. 2. When electromagnet 170 undergoes ACoperation, permanent magnet 178 moves in periodic reciprocal motionalong axis 176.

Reference is now made to FIG. 11 which illustrates an alternativeversion of the linear motion apparatus illustrated in FIG. 5. Here incontrast to the embodiment of FIG. 5, a permanent magnet 190 is disposedin a gap 192 and arranged with respect to the electromagnet core 194such that the motion of the permanent magnet is along an axis 196 and islimited in amplitude by the propinquity of the core 194.

FIG. 11 illustrates two ways of coupling the movable permanent magnet toan external member in driving relationship. A drive shaft 198, coupledto permanent magnet 190 may extend through a passageway formed in core194. Alternatively or additionally a second drive shaft 200 may becoupled to the side of permanent magnet 190 and extend sidewaystherefrom.

The coil arrangement illustrated in FIG. 11 represents an alternative tothe arrangement shown in FIG. 5.

Reference is now made to FIG. 12 which illustrates a vibrating surfacemechanism constructed and operative in accordance with an embodiment ofthe invention. A plurality of individual linear motion mechanisms 210are mounted onto a base 212. Each of the individual linear motionmechanisms may be constructed similarly in all relevant respects to thelinear motion mechanism illustrated in FIG. 2 and described hereinabove.

Each linear motion mechanism 210 comprises an electromagnet 214, apermanent magnet 216 having upper and lower oppositely magnetizedportions and a drive shaft 218 coupled to the permanent magnet. Thedrive shafts 218 of the plurality of linear motion mechanisms are allcoupled to an upper surface 220. The individual electromagnets arecoupled to an AC source in a manner similar to that illustrated in FIG.2 and such that all of the electromagnets 214 operate substantially inphase. When electromagnets 214 undergo AC operation surface 220 iscaused to vibrate relative to surface 212.

Reference is now made to FIG. 13 which illustrates a large amplitudelinear motion device constructed and operative in accordance with anembodiment of the invention. A permanent magnet 230 comprising aplurality of alternating first and second uniform oppositely magnetizedportions 232 and 234 fixedly joined together in side by siderelationship and disposed in a plane is disposed along an axis 236. Atleast two electromagnets 238 and 240 are arranged to define respectivegaps 242 and 244 along axis 236. Electromagnets 238 and 240 are spacedfrom each other along axis 236 so as to lie "out of phase" by one-halfportion length. Thus, as seen in stage a of FIG. 13, when portion 234 isfully aligned with gap 242, one half of adjacent portions 234 and 236 isaligned with gap 244.

Electromagnets 238 and 240 are coupled to a power supply 250, such as aDC power supply whose operation is governed by logic circuitry 252 suchas a commutator switch operated in turn by a sensor 254, such as anoptical or magnetic sensor. Electromagnets 238 and 240 are operatedinterchangeably. Their operation may be understood by considering thesequence of stages a-d illustrated in FIG. 13.

Referring to stage a, it is seen that the junction between portions 232and 234 is centered in gap 244. Electromagnet 240 is then operated toprovide magnetic flux in a direction indicated by an arrow 256, causingportion 234 to become aligned with the magnetic flux direction andcentered in gap 244, resulting in a net movement of one-half portionlength in a direction indicated by an arrow 258. The permanent magnet230 is now positioned as illustrated in stage b. It may be appreciatedthat a stepping operation may be provided by the apparatus of FIG. 13.

Sensor 254 senses the repositioning of the permanent magnet by one-halfportion length and terminates the power supply to electromagnet 240. Asnoted above, sensor 254 may be an optical sensor which may be responsiveto optical coding on the portions of the permanent magnet. Alternativelyit may determine position by sensing the direction and strength ofmagnetization of the adjacent portion of the permanent magnet.

Once the permanent magnet is at stage b, the logic circuitry causespower supply 250 to energize electromagnet 238 to provide magnetic fluxin a direction indicated by an arrow 260, causing portion 232 to bealigned with gap 242 producing a net movement of the permanent magnet byone-half portion length in a direction indicated by arrow 258.

The permanent magnet is now positioned at stage c and the logiccircuitry 252 in response to the output of sensor 254 causes the powersupply to deenergize electromagnet 238 and to energize electromagnet 240to produce magnetic flux in a direction indicated by an arrow 262,causing the permanent magnet to move in the direction indicated by arrow258 by another one-half portion length to stage d.

At stage d, the logic circuitry deenergizes electromagnet 240 andenergizes electromagnet 238 in a direction 264 causing the permanentmagnet to move forward by a further one-half portion length and to bepositioned with respect to the electromagnets in an arrangementanalogous to stage a. Continued forward movement of the permanent magnetin the direction indicated by arrow 258 occurs in substantially the samesequence as described hereinabove.

It is appreciated that the amplitude of motion is limited only by theportion length and the number of portions contained in a given permanentmagnet. The direction of motion may be reversed by reversing thedirection of the magnetic flux produced by the electromagnets at eachstage.

Reference is now made to FIG. 14 which illustrates a balancedcenter-of-mass linear motion mechanism constructed and operative inaccordance with an embodiment of the invention. An electromagnet 270defines a gap 272. Disposed in gap 272 is a first permanent magnet 274having oppositely magnetized portions 276 and 278. Disposed on bothsides of permanent magnet 274 are a pair of second permanent magnets 280and 282, each of which comprises a pair of oppositely magnetizedportions 284 and 286.

It is noted that the magnetization directions of adjacent portions 276and 284 are opposite as are the magnetization directions of adjacentportions 278 and 286. Second permanent magnets 280 and 282 are rigidlycoupled together for common movement by a joining member 288.

The particular arrangement illustrated here prevents the permanentmagnets from being attracted to one or the other pole of theelectromagnet and engage in frictional contact therewith. Such contactwould greatly impair the operation of the linear motion device.

When electromagnet 270 is coupled to a source of AC power for ACoperation the first permanent magnet and the second permanent magnetsmove in reciprocal periodic motion in opposite directions along an axis290 and such that the center of mass of the permanent magnets remainssubstantially static.

Reference is now made to FIG. 15 which illustrates a scaled-up linearmotion mechanism constructed and operative in accordance with anembodiment of the invention. A conventional C-shaped electromagnet 300defines a plurality of substantially identical spaced gaps 302. Apermanent magnet 304 comprising a plurality of oppositely magnetizedportions 306 and 308 arranged in alternating disposition in a straightline is disposed along an axis 310 extending along the gaps 302.

The average position of the permanent magnet with respect to the gaps302 is illustrated and it is noted that the permanent magnet and thegaps are dimensioned and positioned such that every second junctionbetween adjacent portions 306 and 308 is centered in a gap 302. Statedalternatively, each gap is centered on the junction between a portion306 on a first side and a portion 308 on a second side. It is essentialan identically magnetized portion always be on the same side of eachgap.

The electromagnet is connected to an AC power source in a manner similarin all relevant respects to the connection of the electromagnet in FIG.2. During AC operation, the permanent magnet will move in reciprocalperiodic motion along axis 310 with an amplitude (peak to P) equal tothe length of one portion 306 or 308 along axis 310.

Reference is now made to FIGS. 16A and 16B which illustrate a gascompressor constructed and operative in accordance with an embodiment ofthe present invention. The compressor comprises a base 320 whichsupports a compressor tube 322. Disposed in compressor tube are twocylindrical magnets 324 and 326, each formed with a central elongatepassageway through which extends a hollow gas flow tube 328.

Magnets 324 and 326 are disposed in side to side disposition and arearranged such that their respective axes of magnetization 330 and 332are in opposite directions and perpendicular to the longitudinal axis ofcompressor tube 322. The outer diameter of cylindrical magnets 324 and326 is slightly smaller than the inner diameter of the compressor tube322. The magnets are secured together and for sliding engagment insidetube 322 with low frictional resistance on longitudinal bearings 334 and336, typically formed of Rulon, and of outer diameter slightly greaterthan that of magnets 324 and 326.

Gas flow tube 328 effectively bolts together the bearings 334 and 336and the magnets 324 and 326 and is formed with a threaded end 338 whichis engaged by a nut 340. The opposite end of gas flow tube 328 isprovided with a flange 342 which secures it against bearing 334.

Adjacent threaded end 338 there is disposed a spring 344 which whencompressed by magnet movement towards it, urges the magnets back to amiddle position. It is a particular feature of the present inventionthat spring 344 need not be attached either to end 338 or to a gas inlet346 disposed at the end of compressor tube 332 in sealed engagementtherewith as by a washer 348, and which serves as a fixed spring mount.

At the end of gas flow tube 328 opposite to end 338 there is provided aone way valve 350 which only permits gas flow out of the gas tube.

Compressor tube 322 terminates at a second one way valve 352 which ismounted on base 320 by a gas outlet housing 354 and which only permitsgas flow from the compressor tube 322 into the outlet housing. A spring356 disposed in housing 354 forms part of the valve 352 and permits gasflow therepast and via a channel 358 to an outlet 360.

An AC electromagnet 362 comprising a core 364, wound coils 366 and outersecuring brackets 368 is mounted on base 320 by spacer means 370 andconnecting bolts 372. Electromagnet 362 defines a gap 374 across whichthere is produced a magnetic field along an axis 376, alternating indirection. This magnetic field causes reciprocal motion of permanentmagnets 324 and 326 along the axis of the compressor tube, thusoperating the compressor.

According to an alternative embodiment of the invention, the twopermanent magnets 324 and 326 may be replaced by a single permanentmagnet having a magnetization direction perpendicular to the axis of thecompressor tube 322. In this case, however, the spring 344 must beattached to the moving magnet assembly and to the fixed spring supportsince it must pull the magnet back to its starting position.

It will be appreciated that while only a limited number of embodimentshave been illustrated herein, the invention is not limited to what hasbeen particularly shown and described herein. For example, althoughelectromagnets with iron cores have been shown, the invention alsoextends to core-less electromagnets. Thus it is to be understood thatthe invention is limited only by the claims which follow:

I claim:
 1. Apparatus for producing linear motion comprising:a coildefining an electromagnetic field across a gap; and a permanent magnetcomprising first and second sections, magnetized in respective oppositedirections disposed within the magnetic field in said gap for drivingengagement with the electric field, the permanent magnet beingconfigured such that its axes of magnetization lie along its smallestdimension; an iron core about which said coil is wound, said core beingformed of a plurality of layers laminated together, the laminationsbeing stacked along axes perpendicular to the flow of magnetic flux insaid core; and a coil spring coupling said permanent magnet to a fixedsupport, said coil spring extending along a spring axis which isperpendicular to said magnetization axes and parallel to an axis alongwhich the permanent magnet is driven in motion.
 2. Apparatus accordingto claim 1 and wherein said permanent magnet is of high coercivity. 3.Apparatus according to claim 1 and wherein said permanent magnet is ofhigh remanence.
 4. Apparatus according to claim 1 and wherein permanentmagnet is disposed to extend beyond said gap when in its averageposition.
 5. Apparatus according to claim 1 and wherein said coil isalso coupled to a source of D.C. power.
 6. Apparatus according to claim1 and wherein said coil is coupled to said AC source across a capacitor.